A straddle-type vehicle such as a motorcycle having two mufflers provided at left and right sides of a vehicle rear part has been known. In the straddle-type vehicle, for example, the exhaust air having flowed out from each exhaust port of an engine having a plurality of cylinders is collected by a collecting pipe, is distributed to the two mufflers and is discharged to the atmosphere from each muffler.
Also, regarding the straddle-type vehicle having the two mufflers, a straddle-type vehicle has been known which includes an exhaust control valve provided on the way of an exhaust passage between the collecting pipe and one muffler and configured to control a flow rate of the exhaust air to circulate in the exhaust passage.
For example, an exhaust device disclosed in Patent Document 1 includes four individual exhaust pipes connected to respective exhaust ports of a four-cylinder engine, a collecting pipe configured to collect the individual exhaust pipes into one, two exhaust mufflers arranged at left and right sides, and an exhaust air device configured to control flow of an exhaust gas. The collecting pipe is branched at an exhaust air downstream side into left and right branch exhaust pipes, and the left branch exhaust pipe is directly connected with the left exhaust muffler, and the right branch exhaust pipe is connected with the right exhaust muffler via the exhaust air device. The exhaust air device includes a valve configured to control flow of the exhaust gas in an exhaust passage configured to interconnect the right branch exhaust pipe and the right exhaust muffler.
Patent Document 1: Japanese Patent No. 4767183 B
As described above, the exhaust control valve is provided on the way of the exhaust passage communicating with the muffler and a degree of opening of the exhaust control valve is changed in accordance with a magnitude of an engine load, and the like, so that it is possible to improve output and torque characteristics of the engine or to improve an exhaust sound quality. Specifically, in a high load state, the degree of opening of the exhaust control valve is increased to cause the exhaust air to smoothly circulate, thereby increasing the engine output or creating a fascinating exhaust sound, which expresses that the engine is favorably racing. On the other hand, in a low load state, the degree of opening of the exhaust control valve is decreased to increase a back pressure and to suppress lowering of torque during low revolution.
In the straddle-type vehicle having the two mufflers, it is ideal to provide each exhaust control valve at inlet sides of both the muffler. However, if the two exhaust control valves are provided, the number of actuators for operating the exhaust control valves increases, which causes an increase in cost. Further, the number of cables for sending a control signal to the actuators, and the like increases, which makes a layout of components complicated. Considering the demerits, it is proper to provide the exhaust control valve at the inlet side of one muffler.
In a configuration where the exhaust control valve is provided at the inlet side of one muffler, in the low load state, in order to secure the torque during the low revolution, it is necessary to decrease the degree of opening of the exhaust control valve for causing most of the exhaust air to circulate in the other muffler and to thereby increase the back pressure. In order to satisfy the requirements, it is considered to form a bent part at a piping configured to interconnect a point at which the collected exhaust passage is branched toward the two mufflers and the inlet of the other muffler, and to lengthen the piping, thereby presenting a resistance to the exhaust air flowing in the piping. However, it is not easy to implement this configuration.
That is, recently, in order to improve the engine output or to reduce the exhaust sound, a chamber may be interposed between the exhaust pipe connected to the exhaust port (or the collecting pipe connected to the exhaust pipes) and each muffler body. When the chamber is interposed, the point at which the collected exhaust passage is branched toward the two mufflers becomes an outlet of the chamber. The outlet of the chamber and an inlet of the muffler body are close to each other. For this reason, in order to lengthen a piping configured to interconnect the outlet of the chamber and the inlet of the muffler body, it is necessary to increase the number of bent parts to be provided to the piping or to increase a curvature of the bent part. However, in the related art, since the piping is a pipe made of metal, it is not easy to form many bent parts at the piping. Also, if the curvature of the bent part is increased, a weak part is formed at the bent part, so that strength of the piping may be lowered.
Also, a plurality of components such as a footrest and the like is arranged around the outlet of the chamber. The piping configured to interconnect the outlet of the chamber and the inlet of the muffler body should be formed with the multiple bent parts or it is necessary to increase the curvature of the bent part so that the piping is to be arranged not to contact the corresponding components. However, it is difficult to implement such configurations, as described above.